Electric storage batteries (e.g., lead-acid) commonly use thin sheets of microporous material (e.g., polyvinylchloride and polyethylene) known as "separators" between the individual opposite polarity plates of the battery to separate, the plates and prevent dendritic growth or treeing therebetween. Many manufacturers envelope the positive plate of the battery in the separator sheet to prevent edge treeing from one plate to the next. Such envelopes are made by folding the separator sheet in two, placing the bottom edge of the plate in the fold, and bonding overhanging lateral edges of the sheets to each other to form an envelope. Heat sealing, ultrasonic sealing, or pressure sealing techniques have been used for such bonding.
Some batteries include fibrous mats between the plates for a variety of reasons. For example, fibrous glass mats have long been used in heavy duty batteries to apply pressure to the face of the plates for achieving vibration resistance and reducing shedding of the plates. Moreover, gas-recombinant batteries include fibrous glass mats between the plates to immobilize the electrolyte while at the same time permit oxygen transport between the plates for chemical recombination at the opposite plate. Fibrous-polymer mats have also been used for similar purposes. These fibrous mats are typically stacked between the plates but heretofore have not been enveloped about the plates and secured along the lateral edges of the plates as described above for the thin microporous separators, as there has been no battery design need to so envelope the plates. From a manufacturing standpoint, however, these fibrous mats are quite flimsy and accordingly very difficult to handle using automatic equipment. Hence, it would be desirable to envelope the plate in the fibrous separator material to facilitate handling of the material in the plant and, assembly of the battery. However, it has not heretofore been possible to envelope the plate in the same manner as has been done with conventional thin sheet separators, because the techniques used to bond the edges of the thin sheet separators have not been effective to seal the fibrous mat separators and particularly fibrous glass mats.
Accordingly, it is an object of the present invention to provide a unique process for enveloping a battery plate in a fibrous separator material and bonding the edges thereof to themselves outboard the edges of the battery plate. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.